System and method for determining concentration

ABSTRACT

An apparatus to determine the concentration of a target component in a mixture, the apparatus including at least one acoustic transducer located within the mixture, a controller generating a signal for the at least one acoustic transducer that&#39;s generating an acoustic signal in the mixture and transmitting same toward the target component within the mixture, wherein the acoustic signal is generated with a known power level, and a processor for measuring change in the power level of the at least one acoustic transducer as the acoustic signal is transmitted through the mixture, wherein the magnitude of the change in signal power determines the concentration of the target component in the mixture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/AU2016/000394, filed Dec. 9, 2016, and claims benefit of priority ofAustralian Patent Application No. 2015905092 filed Dec. 9, 2015. Thedisclosures of the prior applications are considered part of thedisclosure of this application and are herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a system and method that determines theconcentration of a target component in a mixture such as theconcentration of suspended solids in a mixture. The invention may findparticular use in industries including mining, waste water treatment andpulp and paper manufacturing in which the concentration of suspendedsolids in a mixture at various processing stages is often important toensure processing efficiency.

BACKGROUND OF THE INVENTION

Whilst the system and method of the present invention may find use in anumber of industries, the background of the invention will be describedwith reference to the mining industry and in particular, the frothflotation process. Monitoring and measurement of the suspended solidsconcentration at various stages during the processing of ore is acritical factor in material recovery and overall process efficiency.

Mining involves the extraction of valuable minerals, or other geologicalmaterials, from the earth and a major aspect of any mining process isthe maximization of the recovery of valuable minerals and metals fromlow grade ore at the lowest possible cost. It is recognized that theselective separation of minerals renders the processing of mixed oreseconomically feasible. Froth flotation is a process that has been usedsince the mid-20th century as a recovery means of valuable materialswithin excavated ore that involves selectively separating materials onthe basis of differences in their hydrophobicity—that is, separatinghydrophobic materials from hydrophilic materials.

The froth flotation process is currently used in mining to separate awide range of sulphide, carbonates and oxides which are subjected tofurther refinement to extract and separate metals such as iron, nickel,copper and lead. Froth flotation is also used during the mining ofsilver and gold in which the recovery of such metals from low grade oreis critical to the economic feasibility of gold and silver processing.

Mineral processing involves the stage-wise liberation and flotation ofthe valuable target minerals and metals from the gangue (waste material)in the excavated ore. Liberation is achieved by mechanical means ofcrushing and grinding, known as comminution, after which the liberatedore (of particle sizes typically less than about 3 mm) is subjected tovarious flotation stages known as Roughing, Cleaning and Scavenging inwhich each flotation stage involves the recovery of progressively finermaterial.

As part of the froth flotation process, the ground ore is mixed withwater to form a slurry which is then transferred to a “conditioner” inwhich surfactant is added to the slurry in order to alter thehydrophobicity of the solids. In this regard, the desired mineral to berecovered, i.e., the target material, generally needs to be renderedhydrophobic by the addition of a surfactant and depending on the type ofsurfactant chosen, various minerals may be selectively renderedhydrophobic in order to recover only the desired minerals by frothflotation. In order to recover the desired minerals, the “conditioned”slurry that contains a mixture of hydrophobic and hydrophilic particlesis then introduced to tanks known as flotation cells that are aerated toproduce bubbles to which the hydrophobic target material attaches andtherefore rises to the surface, forming a froth. The mineral laden frothis then removed from the flotation cell, producing a concentrate of thetarget mineral. A stable froth is essential for the efficient recoveryof valuable minerals and frothing agents or “frothers” are typicallyadded to flotation systems in order to enhance and maintain frothstability.

Stage-wise liberation and flotation is required in order to minimize therequired energy input during comminution and hence the processing costs.In this regard, the aim is to recover as much of the valuable coursematerial as possible during an initial flotation step (i.e. Roughing) inorder to avoid grinding the entire excavated ore to finer recoverablematerial. As the rougher concentrate produced during the Roughing stageis of low quality, it must usually be subjected to further processing inone or more Cleaner cells or Scavenger cells.

In the Cleaner cells, the rougher concentrate is subjected to a furtherflotation stage in order to separate any undesirable material previouslyrecovered as part of the Rougher flotation stage. The aim of theCleaning flotation stage is to produce a concentrate that is the highestquality possible and accordingly, the product from the Cleaningflotation stage is referred to as the “cleaner concentrate” or the“final concentrate”.

In addition to, or instead of, progressing the rougher concentrate to aCleaning flotation stage, the rougher concentrate may be subjected tofurther grinding (usually called re-grinding) to achieve completeliberation of the valuable minerals. Due to the lower mass of therougher concentrate as compared with the original excavated ore, lessenergy is required than would otherwise be necessary if the wholeexcavated ore were re-ground. Following re-grinding, the rougherconcentrate may then be subjected to a Cleaner flotation stage (aspreviously described), or a Scavenger flotation stage with the aim ofrecovering any target minerals that were not recovered during theinitial Roughing flotation stage. The Scavenging stage may requirealteration of the flotation conditions to ensure maximum mineralrecovery, or further grinding may be required in order to providefurther liberation followed by a further flotation and recovery step.

During each stage of flotation, the minerals that do not float in thefroth are referred to as the flotation tailings. If appreciable inquality and amount, these tailings may also be subjected to furtherstages of flotation to recover any valuable particles that did not floatduring previous flotation stages. The final tailings after scavengingare normally discarded for disposal as mine fill or transported to atailings disposal facility for long-term storage.

A typical froth flotation system contains many variables related to theequipment design, chemistry and operation of the system. Some equipmentconsiderations include choice of cell type, slurry agitation means,aeration means, cell configuration and control. Some chemistryconsiderations include surfactant type and dosing in addition to frothertype and dosing and system pH. Some operational considerations includewater and air feed rate, mineralogy, particle size, system temperatureand slurry (or suspended solids) density. It will be appreciated thatcareful choice and control of such variables is required in order toensure high mineral recovery and processing efficiency. Further, anydeviations from optimal conditions can lead to a dramatic decrease inmineral recovery, process efficiency and ultimately processprofitability and economic viability.

One of the critical operational variables in a froth flotation system isthe slurry (or suspended solids) density. Currently, the suspendedsolids density of a slurry is generally measured with the use of anuclear density gauge that is externally fixed to the pipe through whichslurry (crushed ore and water) is fed into the conditioner in whichsurfactant dosing occurs. The amount of surfactant added to the slurryis related to the suspended solids concentration of the slurry in theconditioner feed pipe. Since solids (other than the target minerals thatare desired to be recovered) also exist in the slurry entering theconditioner through the feed pipe to which the nuclear density gauge isfixed, such an arrangement tends to overestimate the amount ofsurfactant required. Overdosing the system with surfactant not onlyresults in a wastage of surfactant, but also affects froth quality andmay result in inefficient mineral recovery and lower recovery yields.

Additionally, the suspended solids concentration of the slurry in thefeed entry pipe to the conditioner can vary from 20% (w/v) to 65% (w/v)due to variations in the extracted ore from the mine-site and dynamicvariations of this magnitude can lead to “sanding” of the particles.Sanding refers to the loss of particles due to their “dropping out” ofthe froth suspension when the concentration of suspended solidsincreases above a level that is able to be agitated and therefore keptin suspension, by, for example, a fixed speed agitator.

Current efforts to increase the accuracy associated with measuring theconcentration of the valuable material to be recovered within frothflotation systems involves the use of a “bottle test” in which a sampleof the conditioned slurry in the flotation cell is manually taken inorder to determine the density of the suspended solids. It will beappreciated that manual sampling is a labor intensive and time-consumingprocess and is also not able to adequately monitor dynamic systemchanges thereby reducing the accuracy and usefulness of suchmeasurements.

Another problem associated with measurement of the suspended solidsconcentration using conventional density gauges is that slurries are notonly made up of solid particles, but also include suspended gas bubblesas a result of aeration of the slurry during the froth flotationprocess. Such gas bubbles often interfere with the currently useddensity measurement arrangements of the suspended solids within theslurry mixture.

Yet another problem associated with measurement of the concentration ofsuspended solids of slurries using conventional density gauges is thatscale can often accumulate on the surface of the gauge thereby requiringfrequent cleaning of the equipment that may cause the measurement systemto be unavailable and/or loss of process efficiency.

Accordingly, there is a need for a sampling system and method that isable to dynamically track changes in the concentration of suspendedsolids of slurries such as those that exist in froth flotation systems.Further, there is a need for a control system operable to dynamicallytrack changes in the concentration of suspended solids in slurries andadjust operating parameters of a mineral processing system accordingly.

The present invention seeks to address at least one or more of the abovedisadvantages associated with conventional systems and methods ofmeasuring the concentration of suspended solids in slurries.

The reference to any prior art in this specification is not, and shouldnot be taken as, an acknowledgement or any suggestion, that the priorart forms part of the common general knowledge.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a system configured todetermine the concentration of a target component in a mixture, thesystem including at least one acoustic transducer located within themixture, a controller generating a signal for the at least one acoustictransducer that's generating an acoustic signal in the mixture andtransmitting same toward the target component within the mixture,wherein the acoustic signal is generated with a known power level, and aprocessor for measuring change in the power level of the at least oneacoustic transducer as the acoustic signal is transmitted through themixture, wherein the magnitude of the change in signal power determinesthe concentration of the target component in the mixture.

In another aspect, the present invention provides a control systemconfigured to determine the concentration of a target component within amixture, the system including an apparatus having at least one acoustictransducer located within the mixture, a controller for generating aninput signal for the at least one transducer thus generating an acousticsignal in the mixture and transmitting same for transmission towards thetarget component within the mixture, wherein the acoustic signal isgenerated at a known and fixed power level, and a processor formeasuring a change in the power level of the acoustic transducers as theacoustic signal is transmitted through the mixture wherein the magnitudeof the change in power level is used to determine the concentration ofthe target component in the mixture, wherein the apparatus generates acontrol signal representative of the concentration of the targetcomponent, said control signal used to control one or more additionalcontrollers.

In another aspect, the present invention provides a method to determinethe concentration of a target component in a mixture, the methodincluding the steps of generating a signal for at least one acoustictransducer, thus generating an acoustic signal and controlling the powerof the acoustic signal, measuring any change in the power of the atleast one acoustic signal as the acoustic signal is transmitted throughthe mixture; wherein the detection of a change in the power of at leastone acoustic signal is indicative of the presence of the targetcomponent in the mixture, and wherein the magnitude of change in thepower of the at least one acoustic signal determines the concentrationof the target component in the mixture.

SUMMARY OF EMBODIMENT(S) OF THE INVENTION

It will be appreciated that in embodiments, in order to determine theconcentration of the target component within a mixture, the power of theacoustic signal is initially correlated against varying and knownsuspended solids concentrations within a particular flotation process.It will also be appreciated that the change in power is measured againsta baseline measurement conducted in a clear aqueous medium. Accordingly,the change in power of the acoustic signal correlates with varyingconcentration of suspended solids for a particular flotation process andas such, the correlation may be used to determine and identify varioustarget component concentrations in the mixture during operation of theflotation process.

In embodiments, the system includes two or more transducers located inan array.

In other embodiments, the array is a linear array of transducers formedfrom a single line of transducers although it will be understood thatother configurations of transducers within the array may be used.

In another embodiment, the at least one array includes a plurality ofarrays connectable with each other to form an extended array.

It will be appreciated that any number of transducers may be used.However, in an embodiment, the array includes at least three transducerslocated in a single line to form a linear array.

In embodiments where more than one transducer is included in an array,the measured power of the acoustic signal may be the average power ofthe plurality of transducers.

In an embodiment, the controller is programmed to control two or moretransducers to generate an acoustic signal, wherein the power of the twoor more acoustic signals is the calculated average power of the two ormore signals. It will be understood that in this embodiment, themeasured change in the power level of the two or more acoustic signalsoccurs as the acoustic signal moves through the mixture comprising thetarget component, and is the average change in the power of the two ormore acoustic signals.

In an embodiment, the controller is programmed to generate a signal forthe at least one transducer upon the input of an external command whichgenerates an acoustic signal for transmission into the mixture.

In an embodiment, the controller is programmed to control the at leastone signal to generate a periodic acoustic signal.

In another embodiment, the controller is programmed to control the atleast one signal to generate a continuous acoustic signal.

In an embodiment, the system utilizes high powered, low to mediumfrequency (approx. 20 kHz), transducers that are impedance matched tooperate as sonar transducers within liquid media. The transducers mayhave variable drive levels that are capable of manual operation toproduce different power outputs from the operating diaphragms.

In an embodiment in which three transducers are adopted in a lineararray, the power output of the three transducers is averaged and a 4-20ma analogue output is provided that is proportional to the change inpower output of the transducers.

In embodiments in which a solids concentration profile of the entiretank is required, up to 80 individual transducers may be used, with eachindividual transducer identified and the output from each transducertransmitted, by a communication protocol, to a control system.

The system and method of the invention enables measuring theconcentration of suspended solids over a wide concentration range and inan embodiment, the system is configured to measure suspended solidsconcentration ranging from about 20% to about 65% (w/v).

When producing power outputs greater than 100 watts, the transducersrequire cooling.

When operating the one or more transducers at a fixed voltage level andfrequency in an aqueous medium, it is observed that the transducer poweroutput as measured in clean water increases, proportionally, with anincrease in the amount of solids within the aqueous medium immediatelyin front of the transducer operating diaphragm. Without being bound bytheory, it is considered that the observed change (increase) in powerlevel required to operate the transducers with a fixed voltage andfrequency is caused by “acoustic reflective impedance”. “Acousticreflective impedance” is the ratio of acoustic pressure to acousticvolume flow and it is postulated that acoustic reflective impedancechanges in accordance with the concentration of suspended solids withina liquid medium.

It is further postulated that when an acoustic signal is generated andtransmitted through a mixture and encounters the surface of any solidparticles suspended in the liquid mixture, the signal is reflected fromthe solid particles back towards the operating diaphragm of thetransducer(s). Accordingly, as the solids concentration within a liquidmedium increases, a proportional change in acoustic reflective impedanceand a proportional change in transducer power output is observed.

In an embodiment, the liquid layer is agitated and aerated in theflotation tank, such that gas bubbles ascend through the liquid layer toproduce a froth layer. Whilst the acoustic impedance changes due to anyincrease in the suspended solids concentration and the requiredtransducer power output increases, it has been noted that the acousticimpedance and transducer power output remains substantially unaffectedby the presence of gas bubbles within the liquid medium. It is thoughtthat this may be due to the fact that the gas bubbles, unlike solidparticles, are able to be compressed and disperse on contact with theacoustic signal and therefore do not contribute to the acousticimpedance and reflection of the acoustic signal back to the transduceroperating diaphragm.

Accordingly, the system and method of the present invention may be usedin various embodiments to determine the suspended solids concentrationwithin a liquid medium even in the presence of gas bubbles that areproduced as a result of aeration of the medium during the frothflotation process.

The transducers may also be controlled to produce high power outputsthat assist in eliminating accumulation of scale from the operatingdiaphragm immersed within the mixture. In embodiments, the controller isfurther adapted to control each transducer to operate in a cleaning modefor generating a signal which forms cavitation in the mixture, suchthat, if one or more substances within the mixture has accumulated at ornear the transducer, the cavitation removes at least some of theaccumulation from on and/or near the transducer. In this regard, thepulse amplitude of the signal is sufficient to cause a phenomenon called“rarefaction”, which in turn causes cavitation. The cavitation mayresult in any accumulated substance dissolving, if it is a substancesoluble in the slurry medium (usually water), and if the cavitationenergy is sufficient to effect such dissolving. The cavitation mayresult in an accumulated substance being displaced, if it is not solublein the slurry medium, for example, oil, grease and scale.

It will be appreciated that the system and method of the invention maybe used to determine the concentration of a target component within amixture, for example, the concentration of suspended solids within aslurry. In embodiments, the slurry is contained within a flotationvessel in which valuable material (ore) is separated from waste materialor gangue.

In another aspect, the present invention provides a system configured todetermine the suspended solids concentration of a slurry, the systemincluding at least one acoustic transducer located within the slurry, acontroller generating an input signal for the at least one transducerthus generating an acoustic signal in the mixture and transmitting samefor transmission towards the suspended solids within the mixture,wherein the acoustic signal is generated at a known and fixed powerlevel, and a processor for measuring a change in the power level of theacoustic transducers as the acoustic signal is transmitted through theslurry wherein the magnitude of the change in power level is used todetermine the concentration of the suspended solids in the slurry.

In yet another aspect, the present invention provides a method ofdetermining the suspended solids concentration of a slurry, the methodincluding the steps of generating in at least one transducer, anacoustic signal at a known and fixed power level, measuring a change inthe power level of the one or more acoustic transducers as the acousticsignal is transmitted through the slurry, wherein the detection of achange in the power level of the one or more transducers is used toindicate the presence of suspended solids in the slurry, and wherein themagnitude of the change in the power level of the one or moretransducers is used to determine the suspended solids concentration ofthe slurry.

In an embodiment, the slurry is contained within a froth flotation tankand includes a bottom-most liquid layer, an intermediate froth layer anda top-most gaseous layer wherein the one or more transducers of thearray are submerged within the bottom-most liquid layer of the slurry.It will be appreciated that one of the benefits of the presentlydescribed system and method of the invention is that the concentrationof suspended solids within the slurry liquid layer may be continuouslymonitored and measured with sufficient accuracy and without the need forany manual handling or system downtime during suspended solids analysisand/or equipment maintenance. Accordingly, a system operator may belocated geographically remote from the tank and still ensure that theprocess is running optimally and at peak efficiency.

In other embodiments it is contemplated that the system and method canbe arranged so as to give feedback of the suspended solids concentrationin the liquid layer of the flotation tank directly to an automated inputmeans. In this regard, the processor may be configured to sendinformation to a controller for controlling, for example, dart valves,which regulate flow of liquid into the flotation tank; agitators(including impellers located in the tank); or; aerators (includingaeration tubes connected to the tank), or any other devices forregulating or controlling the operation of the tank. In this regard, theflotation tank can be made autonomous or semi-autonomous.

In an embodiment, the liquid layer is a slurry or pulp containing layerof at least one mineral. The flotation tank could be used for processingvarious products from mining and other geological extraction methods,such as: copper, molybdenum, gold, silver, lead, nickel, iron ore, coal,potash, oil and oil sands, gypsum and many other substances. However, itis also contemplated that the system and method of the invention couldbe applied to other processes outside of minerals processing, such asfood or beverage production or other types of manufacturing wheremeasurement of the suspended solids concentration of a slurry byacoustic measurement can provide an advantage over other types ofmeasurement. It is important to note that the system and method of thepresent invention may be used to determine the concentration ofsuspended solids in a liquid irrespective of whether or not the liquidis subjected to aeration. However, it is particularly advantageous thatthe system and method of the present invention is capable of determiningthe concentration of suspended solids in a liquid that is subject tovarying levels of aeration without any noticeable effect upon thedetermination of the concentration of solids in the liquid. It ispostulated that the presence of air bubbles in a liquid medium does notaffect the result of the determination since the air bubble does notpresent any acoustic reflective impedance and hence does not cause anysignificant change to the power required to generate and transmit theacoustic signal through the mixture.

Embodiments of the invention will now be described in further detailwith reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a vessel and system in accordancewith an embodiment of the present invention;

FIG. 2 is a partially cut away perspective view of a flotation tank withtransducer array in accordance with an embodiment of the invention;

FIG. 3 is a perspective view of an alternative embodiment of an arrayhaving three (3) transducers in a linear configuration:

FIG. 4 is a perspective view of a single array with eight (8)transducers in an array according to an alternative embodiment of theinvention;

FIG. 5 is a perspective view of an extended array of a plurality ofarrays, in accordance with yet another embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION

The system according to any embodiment of the invention and as shown inFIG. 1 will now be described. This figure shows flotation tank 32 withliquid layer 36, a froth layer 38 and an air layer 40 with interfaces37, 39 therebetween. Liquid layer 36 also has solids 41 suspendedtherethrough.

As is further shown in FIG. 1, extended array 30 is submerged withinliquid layer 36 comprising suspended solids 41. FIG. 1 further showscontroller 42 for controlling the operation of extended array 30. Alsoshown is monitoring apparatus 44 (which in embodiments may also includethe processor for processing the power output from the transducerarray). It will be understood that the monitor may be geographicallyproximal to the flotation tank, or remote.

With reference to FIG. 2, further features of flotation tank 32 isshown, this time without the controller, processor or monitoringapparatus shown in FIG. 1. As shown in FIG. 2, tank 32 also has anaerator 110, including a motor 112, a shaft 114 and blades 116. Tank 32also includes a submerged array of an extended array 30B of transducers12 within liquid layer 36 which are used to conduct online sampling ofthe suspended solids 41 concentration within liquid layer 36. In thisembodiment, extended array 30B includes two component arrays 10 eachwith eight transducers 12 arranged in a single line to form an extendedarray of a linear configuration. The array 30B is substantiallyvertically mounted in tank 32 and therefore spans the height of theliquid layer 36 so as to obtain a measurement of the suspended solidssubstantially throughout the entire liquid layer 36.

Whilst the extended array 30B shown in FIG. 2 has 16 transducers intotal (across the two array components 10 each with eight transducers 12within the extended array 30B), it will be appreciated that any numberof transducers may be adopted in the system of the invention rangingfrom a system with a single transducer to a system having an array ofabout 80 transducers for very large tanks where a total solidsconcentration profile of the entire flotation vessel is required.

In an embodiment, the system includes three transducers 12 located in anarray 10A as shown in FIG. 3. In certain embodiments, the measured poweroutput of the transducers is the calculated average of the power outputacross the plurality of transducers and in the embodiment shown in FIG.3, the measured power output is the average power output across allthree transducers 12. FIG. 3 also shows transducers 12 arranged inhousing 14.

In another embodiment shown in FIG. 4, the system includes transducerarray 10B including eight transducers 12, mounted in the transducerarray housing 14B in a single line, and closely spaced (or abutting eachother). The transducer array 10B may form an array component in anextended array 30B (see FIG. 2).

FIG. 5 shows an embodiment wherein four transducer arrays 10B formtransducer array components, and are connected together so as to form anextended array 30C. The array components 10B are connected together viabolt holes 22 and connecting bolts 24. However, it will be understoodthat there may be other means of connecting array components 10Btogether so as to form the extended array 30C. A bus (not shown) maydata connect the array components together, so that data is transmittedbetween the arrays, the transducers of the arrays, the controller andthe processor. However, an efficient design may include only onecontroller and one processor for the system and method of the invention.

In embodiments, the aerator can be controlled by the system processor soas to set the speed of rotation, and thus the amount of aeration. Thiscan control the amount of froth production and alter the suspendedsolids concentration within the slurry. In some other types of flotationtank, the aeration is provided via aeration tubes in which air is pumpedinto the liquid. These aeration tubes can also be controlled by theprocessor to regulate aeration in the tank.

Referring once again to FIG. 1, froth layer 38 containing the mineralconcentrate may be periodically removed from tank 32 through pipe 33into a collection vessel such as a launder (not shown) where furtherprocessing of the mineral concentrate occurs. In embodiments, system 1,through the system processor, may also control the rate at which themineral concentrate is removed from tank 32.

The feed rate of water and/or mineral material to be processed into tank32 may also be controlled by the system processor. It will beappreciated that in order to achieve optimum process efficiency andoperation, the suspended solids concentration within a flotation tank istypically maintained at 30-40% (w/v) suspended solids. The ability toconduct continuous online sampling of the suspended solids concentrationwithin the tank therefore allows continuous and rapid adjustment of theprocess conditions. For example, the feed rate of water and/or mineralmaterial into the tank may be continuously adjusted in response to theonline sample readings of the suspended solids concentration usingsystem 1, so as to maintain the suspended solids concentration withintank 32 within an acceptable concentration range.

In embodiments, transducers may be Commercial Off-The-Shelf (COTS) typeproducts. Often such transducers have their own outer protection and/orcasing, which may be suitable for mining applications. The system andmethod may provide additional protection by using an outer casing orhousing, which also provides protection for any electronics, along withproviding extra protection for the transducers. In some embodiments,spacers in the outer casing/housing may be filled with a substance, suchas an epoxy resin, for reinforcement of the casing/housing in the highpressure conditions of the flotation cell/flotation tank.

Where it is desired to provide an extended array, the array components(transducer arrays) are connected with each other so as to form anextended longitudinal array. In such an embodiment, there may beprovided a bus connection between the array components (array modules).It will be understood that any such bus connections, along with allother electronic components situated in the flotation cell/flotationtank, must be protected against the conditions produced by substances inthe flotation cell/flotation tank, and so must be enclosed in the arraycomponents, and must also be enclosed when the array components areconnected together to form the extended array.

In an embodiment, the system may include a housing for the array. Thehousing may be made from glass-reinforced propylene or ABS. It has beenfound that propylene assists in avoiding scale build-up, and istherefore easier for cleaning of the housing.

In an embodiment, the transducer array, or extended array, may be pulsedso that all transducers in the array produce cavitation forself-cleaning at the same time. This facility may be useful forinter-operation cleaning purposes.

It will be appreciated that improved efficiencies will be gained throughthe ability to continuously adjust and control the aeration rate inresponse to the measured concentration of suspended solids in a mineralflotation process. Such automatic and continuous control avoidsoverdosing with reagent which not only improves the froth structure, butalso improves process economics.

The system and method according to embodiments of the invention will nowbe further described with reference to the following experimental testsconducted to demonstrate the principle of operation of the system andmethod according to embodiments of the invention.

Experimental Test 1—Measurement of Change in Acoustic ReflectiveImpedance (Transducer Power Output) with Change in Surface Area ofPerforated Plates Simulating Varying Target Densities

Test 1(a)—Small Scale Test in the Absence of Medium Aeration

In order to demonstrate the change in acoustic impedance (transducerpower output) with varying target densities, perforated plates ofvarying hole sizes (and hence varying surface areas) were adopted andplaced in front of the operating diaphragm of transducers located withina transducer array immersed in an aqueous medium.

It will be appreciated that the perforated plates with varying holesizes were designed to simulate varying target densities as would beobserved in situations where the system of the invention is used todetermine the concentration (i.e., density) of solids suspended withinan aqueous medium. A practical example of where such a system would finduse is in froth flotation systems that are generally used in mineralsprocessing, wherein the slurry is a dynamic system in which thesuspended solids concentration (i.e., solids density) changes with time.

The test was undertaken in a tank of dimensions H: 600 cm×W: 500 cm×D:400 cm which was filled with water and fitted with a linear array ofthree transducers (as shown in, for example, FIG. 2). No aeration of thetank was performed.

The acoustic transducers were calibrated to 90W in clean water byadjusting the drive voltage level. Each test run was performed with adifferent perforated plate having a specific hole-size (and hencesurface area/simulated solid density). Each plate was immersed in waterand placed in front of the operating diaphragm of the acoustictransducers. In each test run, it was ensured that the perforated platecompletely covered the operating diaphragm of each transducer.

The following results were observed:

% Surface area Measured change in Plate no. Closed Open average Power(W) 1 23 77 116 2 42 58 133 3 60 40 142 4 80 20 160

As is demonstrated by the above results, an increase in transducer poweroutput is observed as the % surface area of the perforated plate (i.e.,simulated solids density) increases.

Test 1(b)—Small Scale Test in the Presence of Medium Aeration

Test 1(a) was repeated, this time, in the presence of aeration in orderto determine the effect, if any, of the presence of gas bubbles on thepower output level of the transducers with varying solids density. Theaeration flow rate was initially lowered to the lowest possible flowrateand then progressively raised to the maximum flowrate.

Each perforated plate (1 to 4—see Test 1(a)) was tested at each aerationlevel and similar results were obtained to those obtained in Test 1(a)with a ±1% change in average power output (W) observed from minimumaeration flowrate to maximum aeration flowrate for all plates 1 to 4.This demonstrates that the system and method of the present invention isindependent of, or unaffected by, the presence of gas bubbles duringaeration of the medium.

Experimental Test 2—Measurement of Change in Acoustic ReflectiveImpedance (Transducer Power Output) with Change in Suspended SolidsDensity (Soil) within an Aqueous Medium

The test was undertaken in an aeration tank of dimensions 3 m high and1.5 m diameter which was filled with water and fitted with a lineararray of three transducers. Medium aeration of the tank was performed.Aeration was performed using sintered filters that produced bubblesconcentration of <3 mm. No air flow rates were measured.

The acoustic transducers were calibrated to 90 Watts in clean water byadjusting the drive voltage level and with rates of aeration varyingfrom minimum to maximum aeration, similar results with the perforatedplates were obtained as compared with Experimental Test 1.

As solids were gradually introduced into the liquid in the tank, changesto the power supplied to the transducers was measured and a similarcorrelation of the solid material in suspension as compared with theinput power to the transducers operating at a fixed and known voltageand frequency.

Solids (soil particles) progressively settle out of the suspension overtime, the average input power to operate the transducers decreasedthereby clearly providing further confirmation of a correlation betweensuspended solids density and transducer average power (W).

Experimental Test 3: Measurement of Change in Power Level with Change inSuspended Solids Density

Testing was performed in a vessel of dimensions (600×400×260 mm) usingthe apparatus of the present invention including three standard 20 kHztransducers.

Testing was performed in 25 liters of water using a suspended solidsconcentration ranging between 0% to 46% (w/v) which covers the range ofsuspended solids concentration typically observed in industrialfloatation cells (i.e., about 20% to 40% (w/v) with an optimal solidsloading of about 30% to about 40% (w/v)).

Uniform mixing of the contents was maintained throughout the vessel withthe use of 2 high speed agitators controlled at an appropriate RPM inorder to maintain the solids in suspension over the concentration rangedtested.

Diatomaceous earth (food grade, 200 microns) was adopted as thesuspended solids during testing (refer to Test 3(a) results). Furthertesting was conducted using food grade diatomaceous earth at 500 micronsparticle size (refer to Test 3(b) results).

Food grade diatomaceous earth (200 and 500 microns) was chosen fortesting as this material is free of impurities and its behaviour andcharacteristics approximate that of copper, gold and nickel particlesthat are typically observed in floatation cells of industrial miningprocesses. The selected particle sizes also cover the particle sizerange typically observed in floatation cells of industrial miningprocesses.

Test 3(a) with Food Grade Diatomaceous Earth (200 Micron)

Whilst agitating the vessel contents at a 0% (w/v) solids in suspension,the acoustic transducers were calibrated at an initial set point of 82watts.

One percent (250 g) increments of diatomaceous earth was tested byweighing each batch and measuring the average power output of threesample pulses of the transducers. The following results were observed:

Measured Watt Solids % (w/v) (Average of three pulses) 0 82 1 93 2 96 398 4 99 5 101 6 103 7 104 8 105 9 107 10 110Test 3(b) with Food Grade Diatomaceous Earth (200 Micron)

Further testing was conducted in which the suspended solidsconcentration within the vessel was progressively increased by 4% (w/v)increments (1000 g).

Diatomaceous earth (food grade, 500 microns) was adopted as thesuspended solids during this further testing. All other parameters wereas for Test 3(a).

The following results were observed with this further test (Test 3(b)):

Measured Watts Solids % (w/v) (Average of three pulses) 14 117 18 126 22133 26 144 30 152 34 159 38 167 42 171 46 176

Accordingly, as the results of Tests 3(a) and 3(b) demonstrate, there isan observable and repeatable trend between the suspended solidsconcentration and the measured power (W) upon transmission of anacoustic, fixed frequency, acoustic pulse, through the slurry. Inparticular, as the suspended solids concentration of the slurryincreases, a corresponding increase in the measured power (W) isobserved.

It will be appreciated that this method of measurement and theobservable trend between suspended solids concentration and measuredpower (W) output may provide mining companies and the like withadvantages in controlling their floatation cell operation, or any vesselin which the suspended solids concentration is to be measured.

Accordingly, the system and method of the invention is not only able toprovide results that are indicative of increased suspended solidsconcentration within a floatation vessel (or the like), but is also aself-cleaning system due to the ability to induce cavitation in themixture (slurry) which is desirable from a processing and operatingefficiency perspective.

In embodiments, the system and method of the invention are substantiallyunaffected by the presence of gaseous medium within the slurry.

In embodiments, system and method enables continuous sampling of thesuspended solids and allows for automatic feedback to the reagent dosingtank for both water addition/subtraction to provide a constant desiredaverage solids concentration (30-40% w/v).

Embodiments of the system are suited for use in the harsh conditionsthat typically exist in mineral processing and is also suited for use inall Sulphides minerals in the flotation cell process.

Any reference to prior art in this specification is not, and should notbe taken as, an acknowledgement, or any suggestion, that the prior artforms part of the common general knowledge.

It will be appreciated by persons skilled in the relevant field oftechnology that numerous variations and/or modifications may be made tothe invention as detailed in the embodiments without departing from thespirit or scope of the invention as broadly described. The presentembodiments are therefore to be considered in all aspects asillustrative and not restrictive.

What is claimed is:
 1. An apparatus for dynamically determining theconcentration of a target component in an aerated mixture, the apparatuscomprising: at least one acoustic transducer located within the aeratedmixture; a controller generating an acoustic signal for the at least oneacoustic transducer operating at a fixed voltage and frequency andtransmitting the acoustic signal toward the target component within theaerated mixture, wherein the acoustic signal is generated with a knownpower level; and a processor for measuring change in the power level ofthe at least one acoustic transducer that is required to maintain the atleast one acoustic transducer at the fixed voltage and frequency as theacoustic signal is transmitted through the aerated mixture, wherein themagnitude of the change in power level of the at least one acoustictransducer determines the concentration of the target component in theaerated mixture.
 2. An apparatus according to claim 1 including two ormore transducers located in a linear array.
 3. An apparatus according toclaim 1 including three transducers located in a linear array.
 4. Anapparatus according to claim 1 where the at least one array includes aplurality of arrays connectable with each other to form an extendedarray.
 5. An apparatus according to claim 1 wherein when two or moretransducers are located in the aerated mixture, the measured power levelis the average power level of the two or more transducers.
 6. Anapparatus according to claim 1 wherein the controller is programmed tocontrol two or more transducers to generate the acoustic signal, whereinthe power of the two or more acoustic signals is the calculated averagepower of the two or more acoustic signals.
 7. An apparatus according toclaim 1 wherein the controller is programmed to generate the acousticsignal for the at least one transducer upon input of an external commandwhich generates the acoustic signal for transmission into the aeratedmixture.
 8. An apparatus according to claim 1 wherein the controller isprogrammed to control the acoustic signal to generate a periodicacoustic signal.
 9. An apparatus according to claim 1 wherein thecontroller is programmed to control the acoustic signal to generate acontinuous acoustic signal.
 10. An apparatus according to claim 1wherein the apparatus utilizes high powered, low to medium frequencytransducers.
 11. An apparatus according to claim 1 wherein the targetcomponent is suspended solids and the apparatus is configured to measuresuspended solids concentration ranging from about 20% to about 65%(w/v).
 12. An apparatus according to claim 11 wherein a substantiallylinear relationship is observed between the suspended solidsconcentration and the measured power level.
 13. An apparatus accordingto claim 1 wherein the apparatus is used to determine a suspended solidsconcentration within an aerated mixture, wherein the change in powerlevel is substantially unaffected by the presence of a gaseous mediumwithin the aerated mixture.
 14. An apparatus according to claim 1wherein the controller is adapted to control each transducer to operatein a cleaning mode for generating the acoustic signal which formscavitation in the mixture.
 15. A control system configured todynamically determine the concentration of a target component within anaerated mixture, the system including an apparatus comprising: at leastone acoustic transducer located within the aerated mixture; a controllerfor generating an acoustic signal for the at least one transduceroperating at a fixed voltage and frequency and transmitting the acousticsignal for transmission towards the target component within the aeratedmixture, wherein the acoustic signal is generated at a known and fixedpower level, and a processor for measuring a change in the power levelof the at least one acoustic transducers that is required to maintainthe at least one acoustic transducer at the fixed voltage and frequencyas the acoustic signal is transmitted through the aerated mixturewherein the magnitude of the change in power level of the at oneacoustic transducer determines the concentration of the target componentin the aerated mixture; wherein the apparatus generates a control signalrepresentative of the concentration of the target component, saidcontrol signal used to control one or more additional controllers.
 16. Amethod for dynamically determining the concentration of a targetcomponent in an aerated mixture, the method comprising the steps of:generating an acoustic signal for at least one acoustic transduceroperating at a fixed voltage and frequency; measuring change in thepower level of the at least one acoustic transducer that is required tomaintain the at least one acoustic transducer at the fixed voltage andfrequency as the acoustic signal is transmitted through the aeratedmixture; wherein the detection of a change in the power level of atleast one acoustic transducer is indicative of the presence of thetarget component in the aerated mixture; and wherein the magnitude ofchange in the power level of the at least one acoustic transducerdetermines the concentration of the target component in the aeratedmixture.
 17. A method according to claim 16 wherein the aerated mixtureis contained within a flotation tank that includes a bottom-most liquidlayer, an intermediate froth layer and a top-most gaseous layer, whereinthe one or more transducers are submerged within the bottom-most liquidlayer of the aerated mixture.
 18. A method according to claim 16 whereinthe aerated mixture is a slurry or pulp containing at least one mineral.19. A method according to claim 16 wherein the change in power level issubstantially unaffected by the presence of gaseous medium within theaerated mixture.
 20. A method according to claim 16 wherein asubstantially linear relationship is observed between the concentrationof the target component in the aerated mixture and the measured powerlevel.